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406 Lawrence K.Wang et al.

also are used when the expected volume of VOC recovery is fairly low, because these
systems cannot be desorbed at the site and must be either land filled or shipped back to
the vendor’s desorption facility. As a result, canister systems do not receive any recov-
ery credits. Another characteristic of the carbon canister system is that the effluent from
the canister is usually not monitored continuously (via an FID, for example). Therefore,
operators of canister systems do not have a clear indication of when a breakthrough
occurs or when the system stops removing the VOC from the airstream.
Becuase carbon canister systems are not desorbed on site and are fairly self-contained
units equipped with vessels, piping, flanges, and so forth, the fundamental variable to
be determined in designing a canister system is the carbon requirement. Examining Eq.
(3) with ND (number of beds desorbing) being zero, the total amount of carbon required
is dependent on VOC inlet loading (M ), total adsorption time (θ ), and working
HAP ad
capacity of the carbon (W ). Therefore, Eq. (3) becomes
c
C = M θ / W (11)
req HAP ad c
From Eq. (11), the total amount of carbon (C ) required for a canister can be deter-
req
mined. The first step is to determine the HAP density (D ) using Eq. (9). The second
HAP
step is to calculate HAP inlet loading, M , using Eq. (4) and the D . These steps
HAP HAP
are shown as follows:
Step 1

D = PM/RT (9)
HAP
Step 2
−5
M = 6.0 × 10 (HAP )(Q )(D ) (4)
HAP e e HAP
The value of M is substituted into Eq (11) and the total amount carbon is then
HAP
calculated. It is assumed in this handbook that this amount of carbon will yield a
removal efficiency of 90%. The required canister number (RCN) is determined by
dividing the total amount of carbon required by the amount of carbon contained in each
canister (typically 150 lb). To ensure sufficient carbon, the quotient is rounded up to
the next whole canister. Once the number of canisters is determined, the design of the
canister system is considered complete in this handbook and costing of the system can
be performed.
4.5. Calculation of Pressure Drops
Figure 3 shows the relationship between the pressure drop and carbon bed depth at var-
ious air velocities. The relationship holds true for any type of carbon adsorption system.

4.6. Summary of Application
At a remediation site, a granular activated carbon (GAC) system is a likely candidate
to be used in a control system because it is a point source having a low concentration
of VOCs emitting into the atmosphere. This system is characterized by its relatively low
capital cost, ease of installation, and ability to control a variety of VOCs. Usually, the
outlet VOC concentrations are required to be less than 10–50 ppmv. Additionally, GAC
system can be either regenerable or disposable types. Another benefit of this system is